Fig. 1: Device structure designed based on photoelectric mechanism.

a Structure schematic of BP in-plane PN homojunction defined by ferroelectric domains. P_up and P_down represent the ferroelectric copolymers are totally polarized upward and downward by piezoresponse force microscopy (PFM) conductivec probe. AC and ZZ axes correspond to the armchair and zigzag direction of BP crystal structure. b Photothermoelectric (PTE) current (I_PTE) in BP device at zero bias. Red (blue) area represents positive (negative) contribution to the PTE current. c PTE current in BP in-plane PN junction device at zero bias. S_N-doped and S_P-doped correspond to the Seebeck coefficient of n-doped BP and p-doped BP. d Band structure of BP in the fresh state and the electrical doped state. Under large electric field, bandgap decreases after electrical doping, and the band dispersion becomes nearly linear in the AC direction while remains parabolic in ZZ direction. e Anisotropic band structure of BP in the fresh state along the AC direction (k_armchair) and ZZ direction (k_zigzag). CB, VB, and E_g correspond to conduction band, valence band and bandgap of BP in fresh state, respectively. f Anisotropic band structure of BP in the doped state along the armchair direction and zigzag direction. CB^*, VB^*, and E_g^* correspond to conduction band, valence band, and bandgap of doped BP, respectively.